1. Field of the Invention
The present invention relates to a synchronizing signal selecting circuit which can select one of various synchronizing signals when various synchronizing signals are inputted to a monitor used for peripheral equipment of a computer, and more particularly it relates to a synchronizing signal automatic selecting circuit designed to select the synchronizing signal which has priority in when a composite video signal and a synchronizing signal are inputted to the monitor at the same time.
2. Description of the Prior Art
As shown in FIG. 1, the conventional synchronizing signal selecting circuit is designed to select one synchronizing signal according to the selection of switches SW.sub.1,SW.sub.2. That is to say, in a state that switches SW.sub.1,SW.sub.2 are short-circuited to fixed terminals a.sub.1,a.sub.2 on one side, horizontal and vertical synchronizing signals inputted to a color signal input terminal G and then synchronized and separated at the synchronizing signal separating circuit 2 are inputted, respectively, to the horizontal synchronizing signal processing circuit 3 and the vertical synchronizing signal processing circuit 4 through the switches SW.sub.1,SW.sub.2. Where switches SW.sub.1,SW.sub.2 are shortcircuited to the intermediate fixed terminals b.sub.1,b.sub.2, the horizontal and vertical synchronizing signals inputted to the synchronizing signal inputted terminals H, V are input, respectively, to the horizontal synchronizing signal processing circuit 3 and the vertical synchronizing signal processing circuit 4 through switches SW.sub.1, SW.sub.2. Additionally in a state where switches SW.sub.1, SW.sub.2 are short-circuited to the fixed terminals C.sub.1, C.sub.2 on the other side, the horizontal and vertical synchronizing signals inputted to the horizontal and vertical synchronizing signals input terminal HV and synchronized and separated at the synchronizing signal separating circuit 5 are inputted to the horizontal synchronizing signal processing circuit 3 and the vertical synchronizing signal processing circuit 4 through switches SW.sub.1,SW.sub.2. Therefore, the conventional circuit has a disadvantage in that the user must select the synchronizing signal by changing the switches SW.sub.1, SW.sub.2 one by one.